Objects exported from Blender contain extraneous wing-like flat faces that don't display in Blender layout and modeling views
This is the result of using ngons. If you add the following edges so that the faces are all quads (on both top and bottom), this should resolve the issue;



As you'd mentioned before, technically all Tris would work too. The issue is that you're dissolving the faces into a face of (what is generally considered) irregular dimensions/vertices. This doesn't cause a problem in Blender because it inherently supports ngons (faces with more than 4 edges/vertices)